I posted this in the race section, some suggested that i post here.
fresh 440/505 and I rebuilt 4 speed probably in 2007 or 2009.

all has been fine until I recently hammered thru the gears going up the highway. After letting out of it and cruising along about 70 (ish) the trans made a loud grinding noise and I had to pull over. (sounded like gears meshing)
after pulling over and manually shifting car while engine off, i restarted it and limped down to the next exit in 1st gear.
Car is fine around town at low speeds, just does this same grinding after hi speed in 4th gear.
I pulled the trans out (23 spline) and took it apart and see nothing obvious.
I looked in the scattershield at the crank/ bronze bushing and see nothing obvious.
I am using a centerforce dual friction clutch.

Has anyone seen this before? I called Wayne at Brewers and he has never heard of this.I am thinking of driving it up to him for a look but would rather get help on here if at all possible.
I can upload pics of the internals but really all looks well except the cluster gear washers cause very slight play, fron output shaft has play( i know this is common due to the nature of the front bearing)and tail shaft has very minimal play. the countershaft keyway has not slipped.

thanks in advance.

John